“I am not sure about 'subsidised' sovereign. Since sovereign is ultimate safety net for entire financial system… the term is I'll suited.”

My answer:

Yes a sovereign, if we ignore inflation and the possibility of being repaid in worthless money, the sovereign represents no risk if it takes on debt denominated in a currency it can print. Which by the way is not the case with the sovereigns in the Eurozone.

But let us assume that in the open market the required risk/cost/inflation adjusted net return for a sovereign in .5% and for the risky SMEs 3%

Then if banks, as it used to be for almost 600 years, had to hold one single capital against the risks of its whole portfolio, and the authorities, or in their absence the markets, allowed banks to leverage 12 times then the risk/cost/inflation adjusted required expected return on equity would be 6% for sovereigns and 36% for SMEs.

BUT, since banks are now allowed to leverage immensely more with safe sovereigns, let us say 40 times and only 12 times with SMEs, the now distorted risk/cost/inflation adjusted expected ROEs are 20% for sovereigns and still 36% for SMEs. So now banks can offer to lower the interest rates to sovereigns and still obtain the risk/cost/inflation adjusted required expected return on equity of 6% for sovereigns, ergo the subsidized sovereign.

OR, since banks could now earn a risk/cost/inflation adjusted expected ROEs of 20% on sovereign debt, then in terms of comparable risk adjustments it would have to earn more than 36% on SMEs, or not lend to them at all, ergo that subsidy to the sovereign, is paid by others who find their access to bank credit made more difficult and expensive as a consequence of the risk weighted bank capital requirements. 

PS. Is there no sovereign risk present when some current rates are negative and central banks work like crazy to produce 2% inflation? 

PS. If you go back in time and start taking about risk-free sovereigns to bankers who sometimes had their head chopped off or were been burned when trying to collect from the sovereigns, they would think you were crazy.